Industrial grade numerically controlled ("NC") tools have reached a high level of sophistication that has emphasized precision, power, and speed. Such tools have become very expensive. Consequently, there is a need for numerically controlled tools for working wood, soft metals, and plastics that would be suited to small shops and home workshops.
The precision and power of current NC machines comes from drive mechanisms that are rugged and highly machined and that typically take the form of a screw-drive, cog-drive, rack and pinion or gear-drive. These drive systems work well, but are inherently expensive, especially when a work area of more than a few feet square is required. While the current art teaches away from it because of elasticity and lack of precision, an alternative means of providing drive power for the linear motion of carriages in an NC system is the use of a cable drive system.
Previous symmetrical cable drive systems have been limited in the load that can be driven because the cable engaged only a portion of the drive drum (e.g. a single quadrant) or required an override of the cable passing around a pulley. As noted above, cable drive systems requiring multiple turns of cable around a drive drum are limited in precision. This limit of precision is due to the differential stretch in the cable as more or less cable is taken up at opposite ends of the carriage travel.
Representative of the art is U.S. Pat. No. 5,368,400 (1994) to Cyphert et al. which describes a marking apparatus for moving a marking head to coordinate positions utilizing two fixed stepper motors performing in conjunction with a cable and pulley drive system.
U.S. Pat. No. 5,363,774 (1994) to Anada et al. describes an X-Y table assembly wherein a linear relative motion can be provided between the first and second tables in the X-direction and between the second and third tables in the Y-direction.
U.S. Pat. No. 5,355,744 (1994) to Yanagisawa describes a two-dimensional drive system having X guides and X shafts and Y guides and Y shafts.
U.S. Pat. No. 5,253,834 (1993) to Sullivan et al. describes a fixture comprising three plates capable of exercising decoupled motion along three angular axis.
U.S. Pat. No. 5,243,893 (1993) to Evans describes a mechanism for positioning a cutting and punching machine relative to a fixed conveyor comprising a carriage supporting the machine for lateral movement and a support track for lateral movement of the carriage.
U.S. Pat. No. 5,216,932 (1993) to Takei describes an X-Y drive apparatus having an X drive unit mounted on a stationary base and a Y drive unit mounted on an X table of the X drive unit.
U.S. Pat. No. 5,207,115 (1993) to Takei describes an X-Y drive apparatus having a pair of stationary pulleys at opposite ends and a table provided with a pair of moving pulleys.
U.S. Pat. No. 5,165,296 (1992) to Yanagisawa describes a combination of a plurality of moving bodies independently moved by each of the two-dimensional drive systems.
U.S. Pat. No. 5,148,716 (1992) to Suda describes a plane motion mechanism having cables connected to drive units through a tension-applying unit.
U.S. Pat. No. 5,145,144 (1992) to Resta et al. describes an apparatus for moving working units along paths having a gear-motor driven carriage moveable horizontally along guides and a gear-motor driven trolley moveable along guides in a second direction.
U.S. Pat. No. 5,040,431 (1991) to Sakino et al. describes a movement guiding device having hydrostatic gas or bearing members with linear motors used as drive sources in the X and Y stages.
U.S. Pat. No. 5,022,619 (1991) to Mamada describes a positioning device having a pneumatic stage supporting a table and movable in the X and Y directions, a moving device using wire and a lifting device for moving the table vertically.
U.S. Pat. No. 4,995,277 (1991) to Yanagisawa describes a two-dimensional drive system having first and second rods traveling along guides which makes two-dimensional movement of a slider possible.
U.S. Pat. No. 4,762,298 (1988) to Wood describes a support and maneuvering device controllable by movement of controlling means.
U.S. Pat. No. 4,423,686 (1984) to Ueno et al. describes a table apparatus having a stacked array of independently driven upper and lower slides driven by a rotation transmission mechanism.
U.S. Pat. No. 4,408,740 (1983) to Kleber describes an apparatus for acceleration-free mounting of a body in a spacecraft having a three axis driving means controlled by scanning units.
U.S. Pat. No. 4,364,695 (1982) to Lenz describes a carving machine with an auxiliary frame having individual motors driving carving tools.
U.S. Pat. No. 4,346,867 (1982) to Dick et al. describes a transport mechanism for an ultrasonic scanner having cables controlling its angular velocity and phase.
All of the prior art machines are very complex and expensive. Each requires very accurately machined parts in order to operate properly. None of the machines is suited for the hobbyist with a modest shop. The present invention solves these problems by providing an accurate yet inexpensive driver and positioning device for the home-shop owner. It can be constructed of readily available materials and yet can operate with repeatable and precise accuracy.